The project's long-term goal is to understand the effects of otologic pathology on mechanisms underlying human cochlear and brainstem auditory processes. We propose a mechanism-based approach that will provide (1) critical neuro-patho-physiological information, (2) a scientific framework for early diagnoses of difficult-to-identify otologic diseases, and (3) measures that will help assess the effectiveness of treatments. We use newly-developed non-invasive auditory brainstem response (ABR) measures to investigate known and hypothesized pathological changes in the mechanisms underlying specific processes in the peripheral auditory system caused by small acoustic tumors, microvascular compression of the cochleo-vestibular nerve, and Meniere's disease/cochlear hydrops. The specific aims are: (1) To continue our work with the Stacked ABR (SABR) and to investigate a chirp stimulus which is a more efficient method of synchronizing neural activity. We will compare the SABR and chirp responses in terms of the sensitivity for screening for small acoustic tumors and to see if a compensation function for hearing loss will improve the specificity of both the SABR and the response to chirp stimuli, (2) To demonstrate that the SABR and chirp response measures can be extended to assessing the presence and the laterality of microvascular compression of the auditory nerve in humans, and (3) To demonstrate that other new ABR measurements investigated in the first funding period can be used not only to diagnose patients with Meniere's disease/cochlear hydrops, but also to monitor the effectiveness of the treatments prescribed. Methods Used: The small tumor and microvascular compression studies use measures of the SABR and responses to chirp stimuli that represent essentially the total amount of synchronous neural activity in response to sound stimulation. The methods for tracking the treatment of patients with Meniere's disease involves special ABR measures. These reflect how cochlear hydrops affect the cochlea's ability to utilize special noises to mask the response to click stimuli. Relevance to Public health: One study will seek ways to improve a comfortable low cost method for screening for small tumors in order to reduce the number of patients who are sent for an MRI scan but do not have a tumor (roughly 999 out of 1000). This will save on healthcare cost and patient anxiety. Another study will provide a method for determining if a patient's hearing and/or balance symptoms are due to a blood vessel that is compressing the hearing and balance nerve, and if so, on which side the compression is occurring. This will reduce the number of needless surgeries and help specify the correct side that should, if desired, be surgically treated. The final study will help monitor treatment of Meniere's disease/cochlear hydrops to determine if the treatments simply affect the symptoms or are truly effecting a cure of the underlying disease.